In a closing method, a work piece constituted by a metal pipe material is rotated and a die is pressed against the work piece while the work piece is heated. Thus, the work piece undergoes plastic deformation as it gradually approaches the die.
A closing machine used in the closing operation comprises an outer diameter chuck that grips an outer peripheral surface of the work piece, and a chuck spindle that drives the outer diameter chuck to rotate together with the work piece. The work piece is closed by pressing the rotating die against the work piece at an offset to the rotating work piece.
The closing method and closing machine described above are disclosed in JP2002- 153930A.
During a closing operation in a conventional closing machine, a die is pressed against a work piece so as to be brought into sliding contact therewith, and as a result, the die rotates in accordance with the work piece, which rotates at a higher speed than the die.
However, during a closing operation in this conventional closing machine, when the die accelerates to catch up with the work piece, the rotation of the die cannot catch up with the rotation of the work piece quickly due to the large inertial mass of a drive system that rotates together with the die, and as a result, a tact time increases. Herein, the tact time is defined as a time required for closing a single workpiece.
It is therefore an object of this invention to provide a closing method and a closing machine with which a rotating die can catch up with a rotating work piece quickly.